1. Field of the Invention
This invention relates to paperboard food packages. Such structures of this type, generally, have lids which can be sealed to the food package without the use of adhesives.
1. Description of the Related Art
One or two serving portions of precooked and/or frozen food are frequently packaged for consumer distribution in paperboard trays. Such trays are folded or pressed from preprinted and die-cut bleached sulphate paperboard blanks or sheets.
Covers for these paperboard trays may take one of several forms including a top flap that is an integral continuation of the same paperboard sheet from which the tray is erected, such a top flap being crease hinged to one sidewall of the tray. Another type of lid is an independent paperboard sheet that is adhesively secured or plastic fuse bonded to a small perimeter flange folded from the upper edge of the tray sidewalls.
As additional factors to the present invention's prior art and development, it should be understood that a typical commercial food tray filling line advances at a rate of 60 to 120 units per minute. Consequently, any step or process in the continuous production line that requires a full stop of the subject unit must be accomplished in one second or less. Other processing steps are performed on a moving unit.
Moreover, once the tray is filled with the food product and the lid is positioned, the tray's inside surfaces are not accessible. Any force applied to a lid flap for sealing against a tray side wall must be less than the crushing capacity of the erected tray. Frequently, only a gentle touch is permissible.
In order to avoid a crushing of the erected tray, the prior art has relied upon both cold set and hot melt adhesives to achieve lid-to-tray seal. Exemplary of such prior art are U.S. Pat. Nos. 5,090,615 to Hopkins et al. and 5,234,159 to Lorence et al. While these two references avoid a crushing of the erected tray, each of these adhesive sealing devices carry respective adverse consequences. For example, cold set adhesives are extremely slow setting and, therefore, incompatible with a production capacity of 120 units per minute. Also, hot melt adhesives have relatively low softening temperatures which are incompatible with typical oven temperatures which are used when the food within the package is heated for consumption. These glue systems also add components to the packaging line which can add expense and time to the packaging of the contents. Finally, these glue systems add additional materials for the food packager to inventory. Therefore, a more advantageous food tray would be one which avoided the use of adhesives.
It is apparent from the above that there is a need in the art for a food tray and lid which can be easily sealed together through simplicity of parts and the uniqueness of structure, and which at least equal the sealing characteristics of the prior food trays, but which at the same time avoid the use of adhesives. It is the purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.